Musar do Liczb 16:33

And we find also in Tanna d'bei Eliyahu 16: "Those who smite in secret 'i.e., speakers of lashon hara] and desecrators of the Name in the open and those who cheapen their friends with words, and those who instigate quarrels will, in the end, be like Korach [and his congregation] of whom it is written (Bamidbar 16:33): "And the earth covered them up." And sometimes the punishment for the sin of lashon hara, the gravest sin of all, is askarah [diphtheria], the gravest death of all, as Chazal have said (Berachoth 8a): "Nine hundred and three types of death were created in the world … askarah is the gravest of all." A sign is given here for all who enter the world, that their punishment is indicative of their sin, as stated in Shabbath 33b: The Rabbis taught: "Why does this death (askarah) begin in the intestines and end in the mouth? R. Yehudah b. Ilai answered: "Though the kidneys counsel, the heart deliberates and the tongue formulates, it is the mouth which consummates [the lashon hara]."

When the Talmud in Sanhedrin 108, debates whether Korach and family will be resurrected when the time comes, the expression עדת קרח used there does not include these two hundred and fifty men. They will certainly qualify for resurrection, seeing theirs had been a noble intention. We can deduce this also from the wording in the Mishnah there which reads: עדת קרח אינה עתידה לעלות, which is proven from the verse: ותכס עליהם הארץ, "the earth covered them," an expression of finality (which clearly refers only to those who were swallowed by the earth).